A group called the Imam Shamil Battalion has claimed responsibility for a deadly subway bombing in the Russian city of St. Petersburg and said the attacker was acting on orders from Al-Qaeda, a U.S.-based organization that monitors extremists says.

The claim by the little-known group was originally published by the Mauritanian news agency ANI, which is often used by Islamist militants in West and North Africa to release statements. It was posted by the SITE Intelligence Group on April 25.

The statement said that bomber Akbarjon Jalilov acted on instructions from Al-Qaeda leader Ayman al-Zawahiri in the April 3 bombing, which killed 16 people and injured about 50.

Russian investigators say the attack was carried out by Jalilov, a 22-year-old Kyrgyz-born Russian citizen who was among the dead.

Russian authorities have arrested 10 people of Central Asian origin on suspicion of involvement and said they have "practically established" who ordered the attack, but gave no details.

The group's name suggests that it was established by people with ties to Russia's mostly Muslim North Caucasus, the site of two post-Soviet separatists wars in Chechnya and a continuing insurgency.

Imam Shamil was the leader of Daghestani and Chechen resistance to Russian forces in the 19th century.